I'm thinking that if the universe spins like a merry go round, then the rate of time can be the tangential velocity. To conserve angular momentum, increased mass (enrgy density) causes the radius of the merry go round (manifold) to decrease to provide a constant angular momentum at all points along the manifold. The decreased radius causes a reduced tangential velocity and thus a reduced rate of time. Although the length of space would have to correlate to a one dimensional radius and the direction of time would have to be perpendicular to the three spacial dimensions formed by the manifold in four space. I think that a consequence would be that an expanding universe (an overall decrease in mass density of the universe) would cause time to slow even though a relative decrease in mass density speeds up the time of the localized area.